Neurology-Online

Acute viral encephalitis

definition

Viral encephalitis is inflammation of the brain caused by viruses.
Various pathogens come into question, such as the herpes simplex virus or TBE. Often the symptoms start suddenly, symptoms such as confusion, restlessness, paralysis can occur. Encephalitis is a life-threatening disease and requires rapid therapy.

Acute viral encephalitis

Viruses can enter the central nervous system (CNS, brain and spinal cord) in two ways:

either along nerves and nerve roots, e.g. B. of the olfactory nerve / olfactory bulb, optic nerve etc.
or via the blood route (hematogenous), which is far more common. Here the viruses cross the blood - liquid (nerve water) - barrier or blood-brain barrier. This “barrier” is an (electron-) microscopic filter between the blood vessels and the cerebrospinal fluid (nerve fluid spaces) of the brain, which ensures that no blood components penetrate into the nerve fluid that washes around the brain. Sometimes it happens that this filter is not particularly tight, so that pathogens can more easily cross the barrier, or the pathogens themselves cause inflammation processes in the vessels that make the barrier leak. However, this depends on many, partly factors that are still unknown, for example the aggressiveness (virulence) of the pathogen and the current immune system and susceptibility of humans.

Symptoms of Acute Viral Encephalitis

With a few exceptions listed below, the symptoms of viral encephalitis are similar for most pathogens.
Often the symptoms start suddenly. The temperature is increased and neck stiffness, as occurs in meningitis, is usually absent.
Many patients are clouded of consciousness (that is, not fully conscious) and often show other psychological symptoms such as:

confusion
Restlessness
aggressiveness
Lack of drive

on. Psychosis occurs in half of the cases.

Depending on where in the brain the inflammatory process is predominant, different symptoms occur (neurological focus symptoms). These range from:

Arm paralysis
Leg paralysis
Eye paralysis
Speech disorder
Balance disorders
Muscle stiffness
Epileptical attack

Viral encephalitis is typically preceded by a general viral disease such as rubella, measles, mumps, chickenpox, and rubella.

Therapy and prognosis

The therapy of acute viral encephalitis depends on the pathogen. There is no specific therapy against viruses that also cause our simple viral meningitis such as coxsackie, echo or myxoviruses (e.g. the influenza virus, parainfluenza and mumps virus) and the same recommendations apply as for simple viral meningitis :

bed rest
Pain relievers (e.g. paracetamol)
antipyretic measures

The other, far more dangerous forms of viral encephalitis discussed below are mostly given so-called antivirals. In most cases, antivirals inhibit enzymes that the viruses use to multiply. The range of drugs has expanded continuously in recent years and more and more well-tolerated antiviral substances are coming onto the market (e.g. Tamiflu).

In severe cases, intensive medical treatment may be necessary: respiratory and cardiovascular functions (blood pressure, pulse, possibly artificial ventilation) as well as the water and salt balance are monitored. If necessary, the intracranial pressure can also be continuously measured directly by inserting a pressure probe directly into the ventricular system of the brain.

How contagious is viral encephalitis?

Viral encephalitis can be contagious in different ways, depending on the virus that causes the encephalitis.
In general, it can be said that viral encephalitis is not a common disease. Even so, there are more vulnerable age groups, such as infants and the elderly, who are more likely to develop viral encephalitis. If a person in the immediate vicinity is affected, the infection can occur very easily, which is why it is essential to keep a distance and hygiene measures. For example, if it is viral encephalitis caused by measles, it is naturally more contagious among children and can easily be transmitted to a child. TBE, which is transmitted by ticks, is again more widespread in forest areas than, for example, in a coastal region.

For general information on virus infections, see: Viral infection

Diagnosis of acute viral encephalitis

As with acute lymphocytic (simple) viral meningitis, the nerve fluid (liquor) removed shows almost normal findings. The most important thing here is to test for antibodies, especially IgM antibodies, because these indicate an acute (fresh) inflammation. However, the pathogen is often not reliably detectable.
With the help of the PCR (polymerase chain reaction) the genes of viruses of the herpes group can be detected or excluded. This can prevent a dangerous course with early treatment.

The EEG (electroencephalogram) also gives indications of a circumscribed and general inflammatory process in the brain. This involves applying electrodes to the scalp. They derive the electrical brain waves. The waves and curves of the EEG are always changed in acute viral encephalitis in contrast to the healthy brain.

Imaging methods such as CT (computed tomography) and MRI of the head (also magnetic resonance tomography, "nuclear spin"), which make layer images of the head, are also used. They often only show a general, uncharacteristic swelling of the brain.
They are mainly used to rule out other causes of the symptoms, e.g. a cerebral haemorrhage that needs immediate surgery, a brain tumor, or a sinus vein thrombosis.

Only the dangerous herpes simplex encephalitis has a characteristic image in the MRI of the brain.

What can you see of the brain in the MRI?

The MRI is particularly suitable for detecting viral encephalitis.
Signs of this can be made particularly clearly visible in it, much earlier than in a CT examination. Particularly characteristic are early condensed areas in the temporal and anterior lobes on both sides of the brain. These are the areas above the ear and behind the forehead. Dorf there are lightened areas in the MRT image that describe an inflammation of the tissue. The swollen brain substance pushes the surrounding areas to the side, which often depresses the cerebral water spaces. In addition, no clear distinction can be made between the cortex and medulla of the brain in these inflamed areas because the boundaries between these areas are visually blurred.

Read on on this topic:

MRI of the head
MRI of the brain

Virus encephalitis causative agent

The most important viruses here are echo, coxsackie and polioviruses (= enteroviruses), the mumps virus, measles virus and flu virus (parainfluenza virus), TBE virus and the group of herpes viruses.
Rapid diagnosis is life-saving, especially for the herpes simplex virus (HSV). Herpes simplex encephalitis is the only absolute emergency among viral meningoencephalitis.

Herpes simplex virus

The encephalitis caused by the herpes simplex virus is a rare, but a very severe form of viral encephalitis.
Even with rapid therapy, permanent damage occurs in half of those affected. The herpes simplex virus enters the brain mainly through body fluids via the nose and paranasal sinuses and leads to fever, confusion, impaired consciousness and epileptic seizures, among other things. It is therefore important to visit a clinic early on. Acyclovir, a drug that inhibits the herpes simplex virus, is treated here if it is suspected.

Read more on this topic at:Herpes simplex encephalitis

TBE

Early summer meningoencephalitis, or TBE for short, occurs mainly in Central Europe in forest areas such as Bavaria, and is transmitted by ticks.
The TBE virus gets into the blood after a tick bite and initially only flu-like symptoms and a slight fever occur. Three weeks later, about 10% of all those affected develop further symptoms. These include encephalitis with impaired consciousness, headaches and speech disorders, but also paralysis of the arms or urinary bladder and an attack on the liver, joints and the heart muscle. Although there is no curative therapy option, only about 2% die from TBE. There is also a vaccination, which is particularly recommended for people who spend a lot of time in the forest.

Read more on this topic at:Vaccination against TBE

Duration of acute viral encephalitis

Viral encephalitis can last anywhere from a few days to many weeks.
The course of the disease is primarily dependent on the virus causing it and the strength of the patient's immune system, so that hardly any statement can be made about the usual duration of the disease. Usually the first phase of the general feeling of illness, which lasts a few days, is followed by a short phase of improvement. Then, along with the general symptoms, those that are very specific for a brain inflammation also appear. These symptoms can last for many days to weeks.

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